The broad purpose of this proposal is to continue our investigations of electrolyte and acid-base regulation from the unique perspective offered by a large environmental chamber that permits carbon dioxide tension to be fixed in vivo at any desired lvel (15 to 150 mm Hg). The specific objectives may be summarized under three major categories: A. Application of the environmental chamber to areas directly related to studies already completed: 1. Response of normal man to chronic hypoxemic hypocapnia. 2. Intracellular pH during graded degrees of chronic hypereapnia and hypocapnia. 3. CSF composition during adaptation to and recovery from hypocapnia. 4. Cation constraints in the adaptation to and recorery from chronic hypocapnia. 5. The influence of chronic respiratory alkalosis, chronic metabolic alkalosis and chronic metabolic acidosis on the acute CO2 titration curve. B. Utilization of the environmental chamber as a "bridge" between respiratory and metabolic acid-base disturbances: 1. The influence of hydrogen ion concentration on the ability of the kidney to raise low plasma bicarbonate concentration in response to chronic hypotonic volume expansion. 2. The influence of PaCO2 on the renal response to mineral acid loads. C. Use of the chamber to create states of "artificial normality": 1. An examination of standard parameters of renal function during various chronic steady-states of PaCO2. 2. The influence of steady-state carbon dioxide tension on the renal regulation of sodium balance and extracellular fluid volume. 3. Influence of steady-state carbon dioxide tension on the renal regulation of water balance.